There is well known a ceramic microphone wherein a pair of polarized electrodes are provided on the opposite sides of a thin ceramic plate (by, for example, annealing a thin silver plate on the surface of a ceramic plate having a thickness of 0.1 m/m at about 800.degree. C.) and the ceramic plate is attached to a diaphragm which is vibrated by sound waves. The ceramic microphone utilizes a phenomenon generating voltage signals by vibrating the ceramic plate with the vibration of the diaphragm and stressing crystal grains in the ceramic plate.
In prior art, as shown in FIGS. 1 and 2, this type of a microphone is such that a thin metal positive (+) electrode 2 is provided on the front side of a ceramic plate 1 and a thin metal negative (-) electrode 3 on the rear side thereof, the positive electrode 2 is connected to a conductor 5, and the negative electrode 3 is attached to a metal diaphragm 4 in an electrically conductive manner and is connected to a conductor 6 through the diaphragm 4. In such a construction, the value of a capacitor formed between the electrodes 2 and 3, each of which is commonly used and has a diameter of 20-25 m/m, may reach the order of tens of thousands of picofarads.
The output of the microphone is connected to an FET (field effect transistor) circuit through the conductors 5 and 6 and is amplified thereby. The value of the capacitor for connecting it to the FET circuit without sacrificing the S/N ratio, the frequency characteristic, or the sensitivity of the order of tens of picofarads may be sufficient.
Although, in the conventional ceramic microphone, the capacitance between electrodes represents the order of tens of thousands of picofarads, the electrical energy produced is hardly utilized.